Overflow control for breast box of a paper making machine



Oct. 27, 1970 K. WOLF 3,536,581

OVERFLOW CONTROL FOR BREAST BOX OF A PAPER MAKING MACHINE Filed March 8,1967 2 Sheets-Sheet 1 IOA Fig. 4

INVENTOR.

KARL WOLF MAM K. WOLF Oct. 27, 1970 OVERFLOW CONTROL FOR BREAST BOX OF APAPER MAKING MACHINE Filed March 8. 1967 2 Sheets-Sheet 2 INVENTOR. K AQ L WOLF United States Patent 3,536,581 OVERFLOW CONTROL FOR BREAST BOXOF A PAPER MAKING MACHINE Karl Wolf, Heidenheim-Schnaitheim, Germany,assignor to J. M. Voitli GmbH, Heidenheim, Brenz, Germany Filed Mar. 8,1967, Ser. No. 621,660 Claims priority, application Germany, Mar. 16,1966,

Int. oi. nzir 1/02 U .S. Cl. 162259 14 Claims ABSTRACT OF THE DISCLOSUREA closed breast box for a paper making machine having an overflow gutteror trough inside the breast box above the discharge nozzle to skim offfoam from the suspension in the breast box and connected to a drainconduit. An air pump is connected to an air space or cushion in thebreast box above the suspension. Devices in the form of an auxiliarydrain conduit and a line to the atmosphere control the levels of thesuspension in the gutter and in the breast box and, thus, also the airpressure in the air space or cushion.

CROSS REFERENCE TO A RELATED APPLICATION This application is based onGerman application, Ser. No. V 30,645, filed Mar. 16, 1966.

BACKGROUND OF THE INVENTION The present invention relates to a breastbox for paper machines, cardboard machines and similar machines formaking webs from fibrous suspensions in which the breast box isessentially closed off from the atmosphere and is equipped at the oneside of its lower portion with a feed line, and at the opposite side atthe lower portion with a discharge nozzle. The breast box, furthermore,is equipped above the level of the fiber suspension therein with an aircushion in the chamber formed at the top of the breast box which iscreated and maintained by an air pump.

The fiber suspension passes through the discharge nozzle to a wire orother water permeable draining surface. Such machines operate at highoperational speeds whereby the liquid level of the fiber suspensioninside the breast box is rather close to the bottom thereof to avoid thecreation of regions of low suspension velocity in the breast box inwhich fibers could flocculate. A certain pressure is needed for bringingabout an outlet velocity of the fiber suspension issuing from thedischarge nozzle, which velocity will correspond to the speed ofmovement of the member forming the draining surface, and this velocityis brought about, in the main part, by the air cushion maintained abovethe suspension in the breast box by the air pump.

The rate at which suspension passes through such a breast box in a unittime is rather large, often weighing from 500 to 1000 times as much asthe web produced from the suspension. The closed air space of chamberabove the suspension inside the breast box is rather small in relationto the amount of suspension to be handled.

Furthermore, most of the fiber suspensions processed in such breastboxes contain materials which tend to create a foam from air bubbleswhich rise in the fiber suspension and become collected at the surfacethereof inside the breast box. Such a foam is driven towards the frontor nozzle wall of the breast box by the movement of the suspensionunderneath the foam as the suspension flows toward the discharge nozzle.This foam, in known constructions of such breast boxes with an aircushion, often occupies a significant portion of the air space in thebreast box.

Patented Oct. 27, 1970 In order to overcome the disadvantageous effectsof such foam accumulations, and to prevent foam particles from becomingentrained in the suspension as it passes through the nozzle, and whichwould detract from the quality of the web, it has been suggested toplace above the discharge nozzle on the inside of the breast box, anoverflow gutter or trough which extends across the full width of thebreast box and is provided with one or more drain conducts leading tothe outside of the breast box. The overflow gutter is attached to theinside of the front wall of the breast box and has a lip or edge justunderneath the normal level of the suspension in the breast box. Thislongitudinal edge or lip forms the overflow edge which is locatedroughly at the desired height of the suspension inside the breast boxand over which edge, suspension and foam flow into the overflow gutter.

The drain conduit leading from the gutter extends through a wall of thebreast box to the outside, and has its lower end immersed in the liquidin the backwater basin or extending into another container whichcontains liquid and is, furthermore, immersed deeply so as to avoidundesirable loss of air from the breast box. By permitting a smallamount of suspension to flow over the overflow edge into the gutter,foam resting on the suspension also flows into the overflow gutter andis entrained by the suspension therein and carried to the backwaterbasin or other container at the outlet end of the drain conduit andbecomes dissolved in the liquid.

Because the amount of air inside the breast box will unavoidably vary,the suspension level during operation will not always remain at the sameheight, but will undergo some change which will, in turn, producefluctuations in the amount of suspension which flows across the overflowedge into the gutter. Therefore, the amount of the foam which isentrained with the overflowing suspension may be subject to fluctuationand, therefore, there will frequently be an undesirable accumulation offoam at the overflow edge. This could take place, for example, when theamount of suspension passing across the overflow edge becomes reduced toa small amount, or even, reduces to zero.

SUMMARY OF THE INVENTION The present invention has, as a primary object,the solution of the problem of preventing fluctuation in the rate ofoverflow of suspension from the breast box into the overflow gutterthereby to establish stable and uniform foam removal conditions. Furtherobjects of the invention are to stabilize the operation of the machine;to improve the product therefrom.

According to the present invention, this problem is solved by providingthe first drain conduit, or conduits, leading from the overflow gutterwith an overflow control device so constructed and arranged as tomaintain a predetermined or normal liquid level in the overflow gutterand, further, by providing a second drain conduit or tube extendingthrough the first mentioned drain or discharge conduit, the crosssectional area of which is small relative to the cross sectional area ofthe first drain conduit and which has a secondary outlet opening or portat about the plane of the normal liquid level in the gutter andextending angularly through said plane. This second drain conduit ortube leads to a point below the liquid level in a liquid containingcontainer, such as a fluid-filled backwater basin. The upper end of thesecond conduit or tube may be vented to the atmosphere so that a verysmall amount of air can escape continuously from the air space of thebreast box. The amount of escaping air will be reduced when thesuspension level in the gutter rises and will be increased when thesuspension level in the gutter falls because of the change in theexposed area of the secondary outlet opening or port in the secondconduit.

A small change in the rate at which suspension flows over the longoverflow edge brings about a substantial change in the level of theliquid in the overflow gutter, and induces a corresponding change in theopposite sense of the amount of escape air which passes through thesecondary outlet opening or port of the second drain conduit or tubeabout the level of the suspension in the gutter, and induces, in thisway, a change of the suspension level in the breast box in the oppositedirection. In this way, accidental changes of the air pressure insidethe breast box become compensated with a speed and efliciency which hasnever heretofore been accomplished. This effect really prevents anyaccidental change of the suspension level inside the breast box, becauseany changes in the rate at which suspension overflows into the gutterare immediately counteracted by this effect right inside the breast box.The extraordinarily high efficiency referred to comes about because anyaccidental change of the suspension level inside the breast box willproduce a great change in the rate of suspension overflowing into thegutter evenly over the long length of the overflow edge.

The changed total amount of suspension over flowing into the gutter willflow with an unchanged velocity through the first drain conduit. Thus, asmall change of the suspension level in the breast box will result in agreat change in the level inside the overflow gutter, up to from to 50times as great as the change of the level inside the breast box. Thismultiplying, or amplifying effect brings about extraordinarily greatstability of the rate at which the suspension flows into the overflowgutter across the overflow edge, and this way brings about not only auniform and stable removal of the foam from the breast box, but also avery stable suspension level inside the breast box, a constant airpressure in the air space or cushion of the breast box, constant outflowvelocity of the suspension issuing from the discharge nozzle, andimproved quality of the web.

With breast boxes for papermaking machines of a great width, it isadvantageous to place at each side of the breast box a first drainconduit with a section of second drain conduit which is equipped with asecondary outlet opening or port. The two drain conduits may also beconnected together undereneath the breast box by the aid of a horizontaltube to which a common discharge tube is connected. In both arrangementsthe lower ends of these conduits lead to the backwater basin or toanother liquid container. When two first drain conduits are provided, asingle second drain conduit or tube may be provided having a port oropening at the normal suspension level. Such a construction of thesecond drain conduit or tube avoids a construction wherein two secondconduits with separate scondary discharge openings or ports exist whichact independent from each other. Thus, the height of these two openingsmight, in practical operation, show slight differences. Such differencescan be of importance in creating difliculties with respect to a correctcontrol of the amount of overflow from the overflow trough or gutter.

It is proposed, furthermore, by the present invention to construct thesecondary outlet opening or port in the second drain conduit or tube asa vertical slit, or a slit which is inclined with respect to a verticalaxis so as to have a vertical main extension. By such a constructionthere will be available, even with great fluctuations of the liquidlevel in the overflow gutter, enough cross section of the secondaryoutlet opening or port inside the first drain conduit to bring about adischarge of fibrous suspension and of air, to avoid the portion of thesecondary discharge opening or port which lies above the level becomingtoo great even if the liquid level in the first drain conduit drops to avery low level. In this connection, according to a further idea of theinvention, the clear width of the secondary outlet opening or portincreases from top to bottom.

Instead of one such secondary outlet opening or port,

two or more such openings can be placed in the wall of the second drainconduit or tube.

In order to adjust the rate at which suspension flows across theoverflow edge to control the removal of foam arising in the breast boxwith the smallest amount of overflow of suspension into the gutter, eachsecondary outlet opening or port is arranged so that it can be adjustedas to height with respect to the overflow gutter. This could be broughtabout, for example by an orifice restricting member which covers aportion of the secondary outlet opening and which is adjustable tovarious heights.

In operation of the machine, it is of importance to keep the amount ofair which flows to the atmosphere through the secondary outlet openingor port as small as possible. In order to bring this about, according toanother fea ture of the invention, the effective cross sectional area ofat least one secondary outlet opening or port can be adjusted. Thisadjustment can also be made by availing of the orifice restrictingmember referred to. In this way the amount of air which escapes can beadapted to the amount of foam which is to be removed, while, further theadded advantage is realized that, inside the breast box, fluctuations ofthe air pressure are kept at a minimum.

The amount of air escaping at a given overflow of suspension into theoverflow gutter can be adjusted so that it will be only a small fractionof the rated output of the air pump. In this way the air pump will haveenough reserve capacity to compensate immediately for small changes inthe amount of air which escapes when the suspension level in theoverflow gutter changes. The described construction of the secondaryoutlet opening or port reduces air pressure fluctuations inside thebreast box and makes it possible to employ a rather small air pump foradjusting the air pressure in the breast box.

An especially advantageous construction is obtained by placing the one,or the several, secondary outlet opening or openings inside a preferablyvertical second drain tube or conduit which extends into or through thefirst drain conduit. With a construction where the second drain tube orconduit penetrates the first drain conduit, the upper end of the seconddrain tube is closed close to the secondary outlet opening, or openings,so that suspension, foam, and air may flow together through thesecondary outlet opening, or openings, into the second drain tube. Whenthis occurs, the air will squeeze foam through the secondary outletopening, or openings, so that only a small portion of the foam is passedthrough the first drain conduit together with the remainder of thesuspension which is flowing from the overflow gutter. In this way thefoam removal from the breast box is achieved in an ideal manner.

In order to keep the air which has left the box via the secondary outletopening and the air which is expelled from the entrained foam whichbreaks down, away from the backwater basin, it is preferred to let thesecond drain tube pass through the first drain conduit and, preferably,in the vertical direction. The part which protrudes upwardly from thefirst drain conduit serves as an air expulsion tube and preferably runsout into the free atmosphere.

The second drain or discharge tube can readily be connected to the firstdrain conduit 50 as to be adjustable therein. For example, the seconddrain tube can pass through a packing in the first drain conduit whichis equipped with a set screw, and adjustment of the height of thesecondary outlet opening occurs by a simple shifting in the longitudinaldirection of the second drain tube, and the desired position is retainedby a tightening of the set screw.

The adjustment of the elfective area of the secondary outlet opening orport in the second drain tube can be accomplished by having twotelescopically arranged c0- axial tubes, both with ports and onenon-rotatable in the first drain conduit and the other rotatable so thatthe degree of registration of the ports can be varied at will byadjusting the rotatable tube. A lever attached to the rotatable tube canrotate it and a clamp screw can clamp the lever in adjusted position.

Both of the tubes are carried by a frame member slidably guided onguideways stationary on the first drain conduit. The guideways carry ahandwheel threaded to an extension of the tubes fixed in the frame sothat by rotation of the handwheel the tubes are raised or loweredsubstantially vertically in the first drain conduit.

The first drain conduit is formed in parts with one section connected tothe overflow gutter and extending through a side wall of the breast boxand other sections outside the breast box. The sections are preferablyprovided with flanges so the outer sections can easily be put in placeon the inner sections and removed therefrom and, together with the tubesand the adjusting mechanism therefor, can form a unit ready forinstallation. The said sections form a horizontal header portionperipherally closed and closed at the outer end. The first drain conduitalso includes a portion leading downwardly from the outermost one ofsaid sections.

The device according to the invention also renders it possible tooperate the breast box with the air cushion at a pressure which is lowerthan atmospheric, if the second drain conduit or tube which is providedwith the one or the several secondary outlet openings does not open tothe atmosphere and immerses with its free outlet end into the backwaterbasin or into another deep container which is filled with liquid.

The upper end of the second drain conduit or tube in this case isconnected by a conduit to the air pump which acts as a vacuum pump. Intothis conduit there may be placed a trap for entrained liquid, the liquiddischarge tube of which also immerses deeply into a liquid container,such as a backwater basin. Another conduit acting as a pressure conduitleads from the pump to the atmosphere. If both the conduits of the airpump are connected to the air space at the top of the breast box, and ifeach conduit is provided with a threeway stop cock with a side outlet,then it will become possible, by a simple adjustment of the two threewaystop cocks, to operate the breast box with pressure below atmospheric orwith a pressure above atmospheric. During operation with asubatmospheric pressure. the suction conduit is connected to the airspace or cushion in the breast box, and the pressure conduit isconnected to the atmosphere. During operation with a pressure higherthan the atmospheric, the suction conduit is connected to theatmosphere, and the pressure conduit is connected to the air cushion inthe breast box.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thepresent invention will be readily apparent from the followingdescription considered in relation to the showing in the accompanyingdrawings, wherein:

FIG. 1 is a perspective view, somewhat schematic, of a breast box withan air cushion and an overflow gutter according to the presentinvention;

FIG. 2 is a vertical section through the first drain or dischargeconduit and second drain or discharge tube showing how the tube could beadjusted;

FIG. 3 is a section on line III-III of FIG.2; and

FIG. 4 shows a modification wherein the breast box is under less thanatmospheric pressure.

DESCRIPTION OF THE OPERATION OF THE PREFERRED EMBODIMENTS In FIG. 1, theclosed breast box 1 of a papermaking machine, has an air cushion abovethe suspension level 3 in a chest 2. A feed line 4 feeds the fibersuspension to the breast box 1 from a source which is not shown. Thesuspension is supplied in homogeneous condition into chest 2 at thebottom at the rear wall 6, remote from the discharge nozzle 5 at theforward end, and which supplying occurs with the interposition of astock distributor 7, and the distribution occurs across the full widthof the paper making machine. The suspension then flows in a rather thinlayer above the bottom 8 of the chest 2 toward the discharge nozzle 5.The suspension leaves the discharge nozzle 5 in a layer which has auniform thickness across the full machine width, and is delivered to adraining member, such as a wire 30, which approaches the dischargenozzle 5 over the breast roll 29.

The layer of suspension is dewatered through draining member or Wire 30and the fibers and other solids of the suspension become deposited uponthe surface of draining member or wire 30. The liquid, with a small residual amount of fibers and solids, passes through the meshes of thedraining member or wire 30 as the so-called backwater, into a backwaterbasin 20 which is located underneath the machine.

The air cushion, which is present inside the chest 2 above thesuspension level 3, is maintained by the aid of a motor-driven air pump9, a suction conduit 12 leading to pump 9, and a discharge conduit 13leading from pump 9, each of which carries one threeway stopcock 10, 11,each fitted with a valve means 10a, 11a. Conduits 12 and 13 areconnected with the air space or cushion in the chest 2 above thesuspension level 3 as by leading through the back wall 6 or the top wall14 of the chest 2.

The threeway stopcocks 10, 11 serve for adjusting the effect of the airpump 9 on the air cushion above the suspension, depending upon wetherthe air cushion operates at higher than atmospheric pressure or at lessthan atmospheric pressure. The breast box can, of course, be operated atatmospheric pressure.

During operation with'higher than atmospheric pressure, the air pump 9draws air through the lateral port of the threeway stopcock 10, adjustedat this time to close the end of conduit 12 leading to the breast box,and the air drawn in by the pump then passes through the conduit 13 intothe air space. An excess of air supplied by the pump may be returnedinto the atmosphere by an adjustment of the threeway stopcock 11 topartially open the lateral port thereof.

During operation with a subatmospheric pressure in the air cushion, theair is drawn through conduit 12 from the air cushion and the threewaystopcock 10, and, by a partial opening of the lateral port of thisthreeway stopcock, air may be admitted from the atmosphere. The pumpedair is expelled through the lateral port of the threeway stopcock 11,into the atmosphere, the end of conduit 13 leading into the breast boxat this time being blocked.

When the suspension is transported, it will entrain more or less airwhich passes into the chest 2. The air will rise inside the suspensionas it flows through the upwardly directed portion of the stockdistributor 7, and accumulates at the suspension level 3 inside chest 2.Many kinds of paper require fiber suspensions which contain admixtureswhich foam heavily, and the entrained air will create a stiff foam whichbecomes accumulated above the suspension level. Rather large amounts offoam can be created this way.

The volume of the chest above the suspension level is small in relationto the amount of suspension processed, so that, with foaming fibersuspensions, the foam, within a rather short time, will occupy more orless all of the air space in the breast box. This foam is driven by thesuspension, which flows across chest 2 from the stock distributor 7towards the discharge nozzle 5, namely towards the front or nozzle wall15 of chest 2.

In order to remove this foam from the chest 2, it is known to place onthe inside of the front wall 15, in overflow trough or gutter 16 whichextends across the full width of chest 2, and which is equipped with adrain conduit generally indicated at 18 for the discharge of suspensionand foam which flows into the gutter 16. The discharge conduit 18comprises a horizontal header portion which includes a section 18Aextending through the wall of the breast box and connected at its innerend to gutter 16, a section 18B outside the breast box and connected tothe outer end of section 18A by flanges, and a section 18C connected tothe outer end of section 18B by flanges. The header is peripherallyclosed and is closed at the outer end and a portion 19 of the drainconduit leads downwardly from section 18C. The overflow edge 17 which isarranged somewhat underneath the desired suspension level 3, isseparated from the front wall of the chest 2 by said overflow gutter 16to which is connected the drain conduit 18.

Across this overflow edge 17, therefore, there will always fiow a littlesuspension into the overflow gutter 16, thereby entraining the foamwhich floats upon the suspension and exists inside the uppermost layerof suspension. The suspension which passes over into the overflow gutter16, together with the foam, is then passed on by the drain conduit intothe backwater basin which is placed underneath the machine and to whichthe lower end of portion 19 is connected at a submerged location.

Section 18B of the header portion of the drain conduit carries a seconddrain tube 27 which has a secondary outlet opening or port 28 therein.Tube 27 extends through section 18B in vertical direction and port 28 isinside section 18B. The portion 19 of the discharge conduit carries aflow regulating or control valve 23.

Sections 18B and 18C of the header portion of the drain conduit, andvalve 23 all have flanged ends to permit replacement thereof withoutinterrupting operation of the machine on the following text, the drainconduit 18 is referred to as the first drain conduit while tube 27 isreferred to as the second drain conduit, or tube.

An average liquid level 26 inside the overflow gutter 16 is adjusted bythe adjusting of flow regulating valve 23, or by a corresponding flowcontrolling device, as, for example, by a second overflow edge which isplaced underneath the overflow edge 17 of gutter 16 inside the headerportion of the first drain conduit. The change of the position of thisliquid level 26 brought about by irregularities of the amountoverflowing into the gutter 16 will be compensated immediately by theaction of the secondary outlet opening or port 28 as will be describedhereinafter.

The portion 19 of the first drain conduit 18 runs out into a pit 24 ofthe backwater basin 20, at a depth where the pressure is greater thanthe greatest pressure head which might occur in chest 2. This can bedone because the level 25 of the backwater is kept constant in a mannerknown per se. This provision insures that no air can escape from chest 2via portion 19 of the first drain conduit.

The small second drain conduit or tube 27, which is small in comparisonto the internal diameter of the header portion of the first drainconduit 18, passes in the vertical direction through section 18B and hasits open, upper end protruding from the said section. The lower end ofthe second drain tube 27 spills out either freely into the backwaterbasin 20, or is immersed therein.

The vertical second drain or tube 27 is provided with a slot-likeopening or port 28 arranged inside section 18B approximately at theheight of the suspension level 26, and extending in a verticaldirection. The clear width of the slot-like opening or port 28 increasesfrom top to bottom, so that the upper portion thereof, above level 26,which is located in the air space in the header portion, is narrowerthan the portion which is located below level 26. Thus, a small amountof air from the air cushion of chest 2 continuously flows through theupper portion of port 28 into the atmosphere, which escaped air becomesimmediately replaced in chest 2 by the output of the air pump 9. If,now, for any reason whatsoever, the amount of suspension passing acrossthe overflow edge 17 changes, and which occurs with only a very smallchange of the height of the suspension level 3 inside chest 2, then theliquid level 26 in the header portion will become changed an amountwhich is a multiple of the amount of change of the level inside thechest 2.

Inside the header portion, the flowing suspension, occopies a crosssection which, in the case of a circular tube, is a circular segment.The Width of this segment in comparison to its width is much smaller,than lateral width of chest 2 is in respect to the overflow height ofchest 2. Therefore, a small change of the amount of suspension whichpasses across the overflow edge 17 will lead to a much greater changeliquid level height 26 in the header portion than the change of thesuspension level 3 inside chest 2, which led to the level change in theheader portion. Thus, even if the rate of suspension passing over theoverflow edge 17 change a very little only, the portion of the secondaryoutlet port 28, which is available for the passage of the air, ischanged greatly, and therefore the amount of air discharged from chest 2also changed greatly. In case the suspension level 3 inside chest 2rises, the rate of overflow through outlet port 28 increases and airflow decreases, and in case the suspension level 3 inside chest 2 drops,the rate of overflow becomes smaller while the air flow increases.

Instead of placing the slot opening 28 in a vertical tube such as seconddrain tube 27 which passes through the section 18B of the header portionof discharge conduit 18, it may be placed directly in the wall ofsection 18B. For the arbitrary adjusting of the rate of suspension whichpasses across the overflow edge 17, the height of the slot opening orport 28 in relation to the height of the overflow edge 17 may bechanged. This may be brought about by placing a movable member 34 whichis also equipped with such a slot opening, or port at the level of thesecondary outlet opening 28 in the second outflow tube 27. By such aconstruction of the secondary outlet opening or port 28, it becomespossible to shut off partially the port 28 by a shifting of the movablemember 35 and in this way to reduce the effective cross section of theport 28. This renders it possible to adjust the rate of overflow to theamount of foam which arises, so that the foam removal from the chest 2is brought about with the smallest possible consumption of suspensionand air.

In the example according to FIGS. 2 and 3, the vertical second drainpipe or tube 27, which carriesthe secondary outlet opening or port 28,passes centrally through the section 18B of the header, and is sealed inplace by sealing rings 33 at regions 31 and 32 where it enters andleaves section 18B. In contrast to the example according to FIG. 1,means are provided for the accurate adjusting of the secondary outletopening or port 28, i.e. for raising or lowering it with greatprecision, and means are also provided for changing the effective crosssection of the port 28 by way of an adjustable tube 34.

Tube 34 telescopically is arranged inside the second drain tube 27 sothat it can rotate and reciprocate therein, and has a collar 35 at itsupper end, above the upper end of second drain tube 27, whereby saidcollar 35 will rest on the upper end of tube 27, with its shoulder 36which faces downwardly. Upon the upper end of the drain tube 27 which isequipped with an external thread, is screwed a frame member 37. There isinserted in frame member 37 from above an air expulsion tube 38, whichdoes not interfere with turning of the tube 34 inside the second draintube 27. Tube 38 is secured by pegs 39 against any turning or shifting.

Machined in frame member 37 is a horizontal incision 40 at the height ofthe collar 35 of the tube 34. An adjusting handle 41 extends throughincision 40 and has a cylindrical end secured by a thread 42 into acorrespondingly threaded bore in the collar 35 of the tube 34. Byturning the tube 34 on the longitudinal axis of the second drain tube 27by the adjusting handle slot-like openings in tubes 27 and 34, which arethe same shape and at the same level, can be varied as to the degree ofregistration thereof from fully open to fully closed. In the oneterminal position of the adjusting handle 41 the outlet opening of thetube 34 coincides fully with the one of the second drain tube 27, sothat the full outflow cross section of the secondary outlet opening orport 28 is obtained. In the other terminal position of handle 41, thesecondary outlet opening or port 2 8 is completely closed because theslot-like opening of tube 34 is completely blocked by the wall of thesecond drain tube 27.

In order to secure the handle 41 in adjusted position, at a certaindistance from the longitudinal axis of the second drain tube 27, athreaded bore is machined into the stem of the adjusting handle 41, intowhich is threaded a wing screw 43. Wing screw 43 passes through anarcuate slit 44 which is located in a metal sheet 45 attached to framemember 37 directly above handle 41, as by welding.

Metal sheet 45, by aid of the wing screw 43, is pressed against theupper side of the adjusting handle 41, and this secures the adjustinghandle 41, and, therefore, tube 34 in adjusted position.

For the accurate setting of the height of the secondary outlet openingor port 28 with respect to the longitudinal axis of the header section18B, and therefore, with respect to the overflow edge 17 of chest 2, theair expulsion tube 38 is provided with an external thread on which isthreaded a handwheel 46 which has an internal thread for this purpose.The hub of the handwheel 46 has a groove 47 into which extend annularprotrusions of a split collar piece 48. This collar piece 48 is attachedupon a yoke or fork 49, which in its center has a bore, through whichthe air expulsion tube 38 freely passes.

This yoke or fork 49 is attached by spaced legs 50, 51 to the lateralsurfaces 52, 53 of the section 18B. These legs 50, 51 servesimultaneously as slide-guides so as to prevent the frame member 37 fromfollowing the turning motion when the adjusting handle 41, or thehandwheel 46, is actuated. For this purpose the metal sheet 45, which isrigidly connected to the frame member 37, is widened towards the legs50, S1 and is equipped with guide pieces 54, 55 which have notches.These notches surround the correspondingly shaped sliding surfaces ofthe legs 50, 51 and slide thereon.

From the foregoing it will be seen that, when the air cushion is under apressure above atmospheric, the rise and fall of the level in theoverflow gutter will respectively increase and decrease the degree ofrestriction to air flow through port :28 and thereby bring about changesin the air cushion pressure which will tend to maintain suspension level3 inside chest 2 constant.

For sub-atmospheric operation, the arrangement diagrammaticallyillustrated in FIG. 4 is availed of. In FIG. 4, the upper end of seconddrain tube 27 is connected to the suction side of pump 9 by an airconduit 60 having therein a liquid-from-air separator 62 which drainsthe liquid separated fromthe air via a conduit 64 to beneath the liquidlevel in a container, such as a backwater basin. Air pump 9 maydischarge into the atmosphere or return a part of the pumped air to theair cushion. It will be appreciated that, with the FIG. 4 arrangement, arise in the liquid level 26 in the overflow gutter 16 will increase therestriction to air flow at port 28 so that the pressure of the aircushion will tend to rise and, instead of aggravating the conditionleading to an increased rate of suspension flow into fl'le overflowgutter 1 6, will tend to compensate therefor. A drop in liquid level inthe gutter 16, similarly, leads to a compensating action by airpermitting a more rapid withdrawal of air from the air cushion by pump9.

FIG. 2 shows how a perforated cap 70 could be provided to screw on theupper end of air expulsion tube 38.

Each of threeway stopcocks 10, 11 referred to has two branches connectedto a main conduit and a third branch connected to a lateral conduit oropening leading to the atmosphere. In a first position of the stopcockflow in the main conduit passes through the valve; in a second positionthe branch of the main conduit connected to the air pump 9 leads to theatmosphere via a lateral conduit or port; in a third position thatbranch of the main conduit connected to the chest 2 is closed off andthe other branch of the main conduit which is connected to the chest 2leads to the atmosphere; and adjusted positions therebetween forrestricting the connection so made.

It will be appreciated that the present invention, in addition toimproving the removal of foam from the suspension, also improves thequality of the web formed because, by maintaining the suspension level 3and the air pressure in chest 2 constant, the rate of flow fromdischarge nozzle 5 to the wire 30 is stabilized and does not vary.

It will further be understood that the supply of suspension from conduit4 is of such a nature as to be sensitive to changes in pressure of theair cushion whereby the compensation action of varying the area or port2 8 available for air flow is effective for holding level 3 in chest 2constant.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions and,accordingly, it is desired to comprehend such modifications within thisinvention as may fall within the scope of the appended claims.

What is claimed is:

1. in a breast box for a paper making machine having an inlet at thebottom in back for the supply of a fibrous suspension to the box and adischarge nozzle at the bottom in front for the discharge of suspensionfrom the box to a fluid pervious draining element or wire, said breastbox having a closed top forming a chamber for entrapment of air in thebreast box above the level of the suspension in the breast box, saidbreast box having an overflow trough extending laterally acrosssubstantially the full width of the breast box on the inside of thefront wall of the breast box above the discharge nozzle and having ahorizontal overflow edge beneath but near the normal level of thesuspension in the breast box so that suspen-.

sion and foam thereon will flow over said overflow edge into saidtrough, and a circumferentially closed first drain conduit leading fromsaid trough through a side Wall of said breast box to outside saidbreast box and including a horizontal header portion at the trough endat about the same level as said trough, a valve in said first drainconduit downstream from said header portion for maintaining thesuspension level in said trough and header portion in a predeterminedhorizontal plane when the suspension level in said breast box is normal;the improve ment comprising; a second drain conduit small in crosssectional area as compared to the cross sectional area of said firstdrain conduit and leading into said header portion and extendingangularly through the said plane, said second drain conduit having anupper end and a lower end which discharges suspension into a containerat a lower level than said header portion, and a lateral opening in saidsec-0nd drain conduit and positioned so as to be intersected by saidpredetermined horizontal plane, and means for causing flow of air fromsaid chamber over said suspension and through said lateral opening insaid second drain conduit to the upper end of said second drain conduit,said means comprising an air pump connected to either said chamber or tothe said upper end of said second drain conduit.

2. A breast box for a paper making machine according to claim 1 whichincludes a pair of three way valves each having a first port meansconnected to a respective side of said air pump and second port meansleading to the atmosphere, one of said valves having third port meansconnected to said chamber and the other of said valves having third portmeans connected to the upper end of said second drain conduit, said pumpmoving air in a direction toward said chamber and away from the upperend of said second drain conduit, and a valve member in each valvecontrolling the communication of the port means of each said valve.

3. A breast box for a paper making machine according 1 1 to claim 1which includes a liquid containing container at a level lower than saidheader portion and in which said second drain conduit leads downwardlyfrom said header portion and has its lower end disposed beneath theliquid level of the liquid in said container.

4. A breast box for a paper making machine according to claim 3 in whichthe said second drain conduit leads upwardly through the top of saidheader portion and has its upper end vented to the atmosphere.

5. A breast box for a paper making machine according to claim 3 in whichthe said second drain conduit leads upwardly through the top of saidheader portion, conduit means connecting the upper end of said seconddrain conduit to the suction side of said air pump, and the dischargeside of said air pump being connected to the atmosphere.

6. A breast box for a paper making machine according to claim 1 in whichat least the portion of said second drain conduit disposed in saidheader portion and said opening therein are vertical.

7. A breast box for a paper making machine according to claim 6 in whichsaid opening is slit-like and widens from top to bottom.

'8. A breast box for a paper making machine according to claim 6 whichincludes means for adjusting said second drain conduit in the verticaldirection in said header portion thereby to adjust the efiective heightof said opening relative to said plane.

9. A breast box for a paper making machine according to claim 6 whichincludes means to adjust the effective area of said opening.

10. A breast box for a paper making machine according to claim 6 inwhich said second drain conduit extends in the vertical directioncompletely through said header portion.

11. A breast box for a paper making machine according to claim 10 inwhich said header portion comprises a plurality of sections in end toend relation and flanged at the opposite ends, one of said sectionshaving said sec- 0nd drain conduit mounted therein and being insertablein and removable from said header portion as a unit.

12. A breast box for a paper making machine according to claim 10 whichincludes a tube telescopically engaging said second drain conduit atleast in the region of said opening, said tube having a second openingtherein corresponding in size and shape to the opening in said seconddrain conduit and adapted for variable registra tion with the opening insaid second drain conduit, and means connected to said tube for movingsaid tube relative to said second drain conduit to vary the degree ofsaid registration of said openings.

13. A breast box for a paper making machine according to claim 12 whichincludes screw threaded means connected to said tube and said seconddrain conduit outside said header portion and operable for adjustingsaid tube and said second drain conduit as a unit in the verticaldirection in said header portion. 7

14. A breast box for a paper making machine according to claim 12 inwhich means are provided externally of said header portion and connectedto said tube for adjusting said tube angularly relative to said seconddrain conduit to vary the degree of registration of said openings andfor locking said tube in adjusted positions thereof.

References Cited UNITED STATES PATENTS 3,092,539 6/1963 Schmidt et al.162-437 XR FOREIGN PATENTS $47,595 10-1957 Canada.

S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner U.S.Cl. X.R. 162-337, 340

